This photo shows the tools I use to apply my ballast. Nothing special but I would specify a glass eye dropper as likely to have a slightly longer life span than the plastic variety. The ballast profile in the background shows an “in progress” stage prior to gluing in place. Gluing tends to darken the ballast as it washes all the dust off from the crushing process the rock goes through in prepartion for sale.
Morpeth In O-Scale 